With the advent of In Vitro Fertilization (IVF), human gametes (sperm, eggs, embryos) are surgically and non-surgically obtained from infertility patients and cancer patients, as well as patients wanting to store their gametes for future use. These gametes are stored in liquid nitrogen and or liquid nitrogen vapor. The expense, both financially and emotionally, of acquiring, storing and later using these gametes for procreation can run very high. Thus, protecting these frozen “assets” is one of the most important roles of the infertility laboratory.
Gametes are stored in liquid nitrogen tanks of various sizes, shapes and constructions. Most importantly, these tanks must include an intact vacuum sealed chamber to prevent rapid loss of liquid nitrogen, and therefore, temperature. Liquid nitrogen exists at −196° C. (˜−400° F.) and while storage in the vapor phase can vary, it needs to be below −150° C. to ensure the integrity of the cryopreserved specimens.
Historically, the monitoring of a liquid nitrogen tank has been considered to require a multi-disciplined approach that typically includes: the daily visual inspection of all tanks, with careful examination of the exterior of the tank for sweating, frost, and/or liquid nitrogen vapors; the use of a dipstick to measure actual liquid nitrogen levels at least twice per week; and electronic monitoring by an electronic alarm system.
Daily visual inspection of and/or the actual measurement of liquid nitrogen levels within a liquid nitrogen tank may be sufficient to discover a slow leak. However, in the event of a more catastrophic and rapid loss of liquid nitrogen from a liquid nitrogen tank, electronic monitoring is typically relied on to detect the problem. Currently, electronic monitoring of liquid nitrogen levels within a liquid nitrogen tank (regardless of size, design or construction) is performed almost exclusively by thermocouple probes that are placed into the opening of the tank. Such a thermocouple probe can be placed in direct contact with the liquid nitrogen in the tank, or may be located above the liquid nitrogen in the superjacent vapor phase. In any case, the thermocouple probe is typically connected to a monitoring system that monitors the temperature within the tank and triggers an alarm if the internal tank temperature exceeds some predetermined value.
A significant shortcoming with respect to the temperature-based monitoring of liquid nitrogen tank internal temperature results from the possibility of detecting an acceptably low temperature even though the tank may already be devoid or substantially devoid of liquid nitrogen due to a leak. More specifically, because liquid nitrogen is so cold and frequently exists at least partially as a vapor within a typical liquid nitrogen tank, the liquid nitrogen vapor may cause the internal temperature of a liquid nitrogen tank to remain at an acceptable level and not trigger an alarm for some period of time after all of the liquid nitrogen has actually leaked out of the tank.
In the case of a significant liquid nitrogen tank failure such as, for example, a tank vacuum system breach (e.g., through external damage to the tank causing a seam to split or a weld to break), rapid liquid nitrogen loss can occur in a matter of minutes, or at most, a few hours. If such a rapid loss of liquid nitrogen were to occur under the circumstances described above, where remaining liquid nitrogen vapor maintains an acceptable tank temperature for some short period of time after a major or complete liquid nitrogen loss, it should be understood that the internal tank temperature will eventually begin to rise rapidly and the integrity of the specimens within the tank will be compromised in short order—quite possibly well before a temperature-based alarm system can issue an alarm and the tank and specimens can be tended to. As most liquid nitrogen storage tanks can hold hundreds if not thousands of specimens, a complete loss of even one tank can be catastrophic for patients and the infertility practice alike.
Unfortunately, real-world examples of such a scenario occurred in March of 2018, when two separate IVF clinics experienced catastrophic specimen loss due to liquid nitrogen tank leaks that were not detected quickly enough. In the case of one of the clinics alone, hundreds if not thousands of specimens completely thawed and were, therefore, a total loss. The resulting emotional toll on patients is impossible to determine, and the financial loss to will certainly run into the millions. And this is not the first time that liquid nitrogen tank failures have occurred in the IVF setting.
From the foregoing description, it should be apparent that there is a heretofore unmet need for a more reliable and faster responding system and method for monitoring liquid nitrogen container levels. Exemplary system and method embodiments disclosed herein meet this need.